1. Field of the Invention
The present invention relates generally to photography and more particularly to a diaphragm and shutter mechanism for exposing film in a camera.
2. Description of the Prior Art
It is desirable in modern cameras to be able to choose from among a number of aperture-shutter speed combinations. One of the simpler forms of exposure control in a still camera that provides a choice of aperture-shutter speed combinations is disclosed in U.S. Pat. No. 4,160,588. In that camera, a diaphragm assembly includes two blades, each of which has a different diameter opening. The larger opening is fixed in the light path of the camera lens to control the amount of light that can pass through such lens. The blade with the smaller opening is manually slidable to locate that opening behind the larger diameter opening, which stops down the lens aperture from f5.6 to f9. A shutter assembly in the camera includes an opening blade and a closing blade, each of which has a similar size opening. The closing blade is normally located in an open or nonblocking position in which its opening is aligned with the light path of the camera lens. Conversely, the opening blade is normally located in a closed or blocking position, blocking the light path of the lens. Upon actuation of a shutter release, the opening blade is spring-urged to an open position, no longer blocking the light path and initiating an exposure interval. A timing circuit, energized in synchronization with movement of the opening blade from the closed position, causes the closing blade to be unlatched after a time period related to the level of scene light received by a photocell in the timing circuit. The unlatched blade is spring-urged to a closed position, blocking the light path of the lens and terminating the exposure interval.
Although providing several aperture-shutter speed combinations, an exposure control such as the one disclosed in U.S. Pat. No. 4,160,588 includes separate dual-blade diaphragm and shutter assemblies, which, owing to their complexity, increases the relative manufacturing cost of such an exposure control. Moreover, with the shutter assembly in this type of exposure control, the opening blade at the end of its spring-urged travel to the open position rebounds off a stop member, possibly causing camera shake during the exposure interval, which may blur the resulting image.
A simplified type of shutter assembly that uses only a single blade to uncover and cover the lens aperture, and which does not cause any camera shake during the exposure interval, is disclosed in U.S. Pat. No. 4,023,192. Upon actuation of the shutter release, the shutter blade is spring-urged continuously from an initial closed position, through an open position, to a final closed position. In this example, any camera shake caused by the shutter blade striking a stop member at the end of its travel occurs after the exposure interval is terminated. However, with this type of shutter assembly, a second or covering blade is included to prevent light from exposing film in the camera during recocking of the shutter blade to the initial closed position. Moreover, the shutter assembly is limited to a single shutter speed.
Another type of shutter assembly that uses only a single blade, but which provides several shutter speeds, is the impact or inertial shutter. This type of shutter assembly commonly employs a single pivoted blade having a circular opening. Upon actuation of the shutter release, the shutter blade is struck by a high-speed impact member and moves from a normally closed position to an open position. The time during which the shutter blade remains in the open position is varied by changing the location of an adjustable rebound stop. At the end of its travel in the open position, the shutter blade rebounds off the stop member and is spring-urged to the closed position. Such rebounding, however, may cause camera shake during the exposure interval.